Drive assembly with overspeed brake

ABSTRACT

A drive assembly brake is mounted in the gearbox connecting a motor driven input shaft to an output shaft, the output shaft being connected by a tubing string to a submersed rotary pump. The gearbox includes an output shaft housing portion defining an oil chamber and an input shaft housing portion defining an oil-free centrifugal brake chamber. The relatively faster moving input shaft carries a centrifugal brake having weight members frictionally engageable with the brake chamber wall when the rotational speed of the input shaft reaches a sufficiently high degree, and the resulting braking action retards the rotation of the input shaft. 
     In one embodiments a split casing gearbox is used having matched passage portions in the faces of the connected gearbox portions to form a lubrication passage system for the shaft bearings.

BACKGROUND OF THE INVENTION

This invention relates generally to drive assemblies for deep-wellsubmersible pumps and particularly to a gearbox brake used in such driveassembly.

Submersible rotary pumps in down-hole locations are connected to thesurface drive assembly by a tubing string which can be of the order of4,000 feet in length. Such an arrangement is disclosed in U.S. Pat. No.4,372,379 (Kulhanek et al.) by way of example.

The surface drive assembly includes an electric motor which drives therotary pump through the medium of the tubing string. In the event thatthe rotary pump overheats, for example due to the lowering of the oillevel, the pump can heat and seize up. When this happens, because of itsextreme length, the tubing string can continue to be rotated by theelectric motor resulting in the twisting of the string with a consequentbuild up of torsion forces in the string. When a rotational limit isreached the motor ceased to turn and at this point the torsion built upin the tubing string can act in reverse causing the string to unwindthereby reverse-rotating the motor drive shaft. The forces unleashedwhen such unwinding occurs can result in the destruction of the surfacedrive assembly and in extreme cases can causes drive pulleys toliterally explode.

In addition to the above, the provision of braking systems for use inconjunction with drive assemblies presents the problem of tamperingwhere the brake system is a separate system and therefore easilyaccessible as well as being susceptible to moisture penetration. Theseproblems are particularly acute where, as here, the system must be leftunattended for long periods of time.

Also adequate lubrication of the shaft bearings is a problem forgearboxes of the type under consideration.

Brakes of various kinds have ben used without solving the problemsatisfactorily. The present invention solves the problem in a manner notdisclosed in the known prior art.

SUMMARY OF THE INVENTION

In accordance with this invention the gearbox which connects the inputshaft and the output shaft of a drive assembly for a rod string isprovided with a brake to retard high speed reverse rotation induced intothe string following seize up of the submersible pump.

Also in accordance with the invention a split casing or clamshellgearbox is provided having a lubrication passage system consisting ofmatched passage portions formed in the connected gearbox faces whichcooperate to form oil conveying passages when the gearbox portions areconnected.

It is an aspect of the invention to provide a gearbox for aright-angularly related input and output shafts and to provide a brakehoused within the gearbox to protect the brake from tampering.

It is another aspect of the invention to provide a centrifugal brakewhich is disposed within the gearbox and provides braking action for therelatively high speed input shaft.

It is yet another aspect of this invention to provide a split casinggearbox which includes spaced input and output shaft bearings and toprovide a spiral passage formed from cooperating grooves in each matchedgearbox portion which communicates with an oil chamber and to providelubricating passage means communicating between said spiral passage andsaid bearings, said lubricating passage means being formed fromcooperating grooves in each matched gearbox portion, lubricating oilbeing pumped from the oil chamber to the bearings by rotation of theoutput shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional elevational view through the drive assemblygearbox;

FIG. 2 is a sectional side view taken in part, through the output shafthousing and in part and the input shaft housing;

FIG. 3 is an elevational view, reduced in size, of a modified gearboxhaving a split casing construction;

FIG. 4 is a plan view of the gearbox illustrated in FIG. 3;

FIG. 5 is a sectional elevational view taken on line 5--5 of FIG. 4, and

FIG. 6 is a sectional side view taken on line 6--6 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now by reference numerals to the drawings it will beunderstood that FIGS. 1 and 2 illustrate a drive assembly generallyindicated by numeral 20 which includes a gearbox 22 providing a meansfor connecting an input shaft 24 to a right-angularly related outputshaft 26. The input shaft 24 includes a pulley 28 driven by an electricmotor (not shown) and the output shaft 26 is connected to a string ofrods 10. The rod string 10 is connected to a submersible pump of thetype disclosed in U.S. Pat. No. 4,372,379 which is incorporated hereinby reference.

The gearbox 22 includes an output shaft housing portion 32, for thecompound output shaft 26, and an input shaft housing portion 34. Theouput shaft 26 includes an outer portion 36, supported by upper andlower bearings 38 and 40, and carries a crown gear 42. A seal 43 isprovided above the upper bearing 38. The ouput shaft 26 also includes acoaxial inner portion 44 which rotates with the outer portion and isconnected to the outer portion 36 at the upper end, by means of adaptor37 and lock nut 39. The said adaptor 37 and lock nut 39 are connected tothe threaded end of the output shaft inner portion, and said innerportion 44 extends downwardly into a support adaptor 100 which isseparately formed from the gearbox 22 and is attached to said gearbox asby bolts 102. The input shaft 24 is supported by inner and outerbearings 50 and 52 and carries pinion gear 54 at its remote end.

An oil stand pipe 46 is disposed coaxially in the space between theinner and outer shaft portions 36 and 44. The stand pipe 46 includes afixedly attached collar 48 at its lower end by which it is carried bythe output shaft housing portion 32. The collar 48 provides a seal suchthat oil is received within and contained between the stand pipe 46 andthe inner face of the output shaft outer portion 36.

The output shaft housing portion 32 is provided with a cover plate 56attached to said housing portion 32 as by bolts 58, and defines an oilchamber 60. A cylindrical dust cover 61 is provided for the outer end ofthe output shaft 26 which is attached to the cover plate 56. The inputshaft housing portion 34 is provided with a cover plate 62 attached tosaid housing portion 34, as by bolts 72, and defines an oil-freecentrifugal brake chamber 66. The chamber 66 is sealed by inner andouter seals 68 and 70 carried by the input shaft housing portion 34 andextending between said housing portion and said input shaft.

A centrifugal brake 80 mounted in the brake chamber includes a hubportion 82 which is fixedly attached to the input shaft 24 as by keyconnection 84. A plurality of arms 86, intregally formed with the hub 82extend radially outwardly from the hub 82, said arms defining shoecompartments 86. The shoe compartments each contain a shoe 88, said shoeincluding a flat inner face 90 attached to a leaf spring 92, as by bolt94, and said spring extending between shoulder portions 96 provided oneach radial arm 86. The shoe 88 also includes an arcuately formed outerface 98 having a brake lining 99 fixedly attached thereto which isengagable in frictional relation with the brake chamber cylindrical wall101 of the input shaft housing portion 34, which is compatiblydiametrically sized.

In a typical installation the gear ratio between the output shaft crowngear 42 and the input shaft pinion gear 54 is 3:1, the input shaft beingdriven typically at up to 1500 rpm. In the event that the submersedrotary pump seizes up and locks in place the length of the rod string,typically 4,000 feet, continues to be rotated at its upper end by theelectric motor with the result that torsion forces are induced into therod string. At a certain point the motor is unable to continue toprovide sufficient power to rotate the rod string further with theresult that the rod string reverses rotation and unwinds at a highspeed. This high speed is considerably in excess of the workingr speedof the input shaft with the result that the centrifugal brake shoes 88move outwardly against the resistance of the springs 92 and the lining99 engages the brake chamber wall 101 and retards the rotational speedof the input shaft to an acceptable speed. When this is reached thebraking action ceases and the shoes return to their original position inwhich there is a gap between the lining 99 and the wall 101.

The gearbox is not limited to the type shown in FIGS. 1 and 2 but canalso be of the split casing or clamshell design as shown in FIGS. 3-6.

This type of gearbox indicated by numeral 122 in FIGS. 3 and 4 is madein two matching portions 124, which are connected together as by aplurality of fasteners 126. Cover plates are not required and access tothe interior of gearbox 122 is achieved simply by separating the splithalves 124. In other respects, the gearbox structural arrangement ofparts is essentially the same as with the type of unit shown in FIGS. 1and 2. In FIGS. 3-6 corresponding reference characters indicatecorresponding parts shown in FIGS. 1 and 2.

As shown in FIGS. 5 and 6, the input shaft 24 is housed in gearboxhousing portion 134 and the output shaft 26 is housed in gearbox housingportion 132.

The housing portion 132 defines an oil chamber 160 but no cover isrequired. Similarly, the housing portion 134 defines an oil freecentrifugal brake chamber 166 which likewise requires no cover andhouses a centrifugal brake 80 as described with respect to theembodiment discussed above. The crown gear and pinion connection is alsoidentical to that described above and the input shaft is supported bybearings 50 and 52 and is provided with seals 68 and 70 and the outputshaft 26 is supported by bearings 38 and 40. The bearings for bothshafts are seated in semi-circular matched grooves provided in thematched portions of the gearbox.

However, distinguishing from the embodiment described above the splitcasing provides means of lubricating the input shaft bearings 50 and 52and the output shaft bearings 38 and 40 which will now be described.

As shown in FIG. 5 the face of each gearbox portion 124 is provided witha lubrication passage system generally indicated by numeral 200consisting of matched semi-circular passage portions which cooperate toform oil conveying passages when the gearbox portions are connected. Oilis supplied from the oil chamber 160 to the input and output shaftbearings 50, 52 and 38, 40 respectively. An intermediate oil reservoir202 is provided below the output shaft lower bearings 40 and a lowerreservoir 204 is provided below the end of the output shaft 26. Thereservoirs 202 and 204 are connected by a spiral passage 206 in thematching gear box portions formed between the two reservoirs. By thisarrangement rotation of the output shaft 26 pressurizes oil from thespiral passage 206 to pump it up into the oil lubrication passage system200.

As shown in FIG. 5 the passage system 200 includes a first branch 210extending between the spiral passage 206 to the output shaft upperbearing 38 sealed at top and bottom by seals 43 and 45. A second branch212 leads to the input shaft bearing 52. Branch 218 interconnects inputshaft bearings 50 and 52 and, through bearing 50, the oil chamber 160.It will be understood that none of the branches of the passage system200 communicates with the brake chamber 166 and that seals 68 and 70prevent ingress of lubricating oil into said brake chamber.

In view of the above it will be seen that various aspects and featuresof the invention are achieved and other advantageous results obtained.While a preferred embodiment of the invention has been shown anddescribed, it will be clear to those skilled in the art that changes andmodifications may be made therein without departing from the inventionin its broad aspect.

I claim as my invention:
 1. In a drive assembly connecting a motor to asubmersible pump by means of a horizontal input shaft connected to themotor and a vertical output shaft rotated at a lower speed by the inputshaft and connected to the submersible pump by a tubing string, animprovement comprising:(a) a gearbox including a first housing portioncarrying the input shaft and a second housing portion carrying theoutput shaft, the first housing portion including a brake-receivingchamber having a brake shoe engageable surface, (b) a brake shoe carriedby the input shaft within the brake-receiving chamber and movableradially outwardly under centrifugal force into engagement with saidbrake shoe engageable surface when the input shaft reversely rotatesabove a critical speed, and (c) means disengaging the brake shoe whenthe input shaft rotates below the critical speed.
 2. A drive assembly asdefined in claim 1, in which:(d) the disengaging means includes aspring.
 3. In a drive assembly connecting a motor to a submersible pumpby means of a horizontal input shaft connected to the motor and avertical output shaft rotated at a lower speed by the input shaft andconnected to the submersible pump by a tubing string an improvementcomprising:(a) a gearbox including a first housing portion carrying theinput shaft and a second housing portion carrying the output shaft thefirst housing portion including a brake-receiving chamber having a brakeshoe engageable surface, (b) a hub attached to said input shaft withinthe first housing portion and including a plurality of outwardlyextending fingers each defining a weight compartment, and (c) aresiliently mounted brake shoe disposed in each compartment, each shoebeing movable radially outwardly under centrifugal force into engagementwith said brake shoe engageable surface when the input shaft reverselyrotates above a critical speed.